The disclosure relates to stress profiles in glasses. More particularly, the disclosure relates to glasses having deep compressive stress profiles. Even more particularly, the disclosure relates to glasses having deep compressive stress profiles and exhibiting non-frangible behavior.
Chemically strengthened glasses are widely used in displays for hand-held electronic devices such as phones, notebooks and the like. Chemical strengthening creates a compressive layer at the surface of the glass and a tensile region in the central portion of the glass. Compressive stress (CS) and depth of layer (DOL) are typically determined from surface stress measurements (FSM) using commercially available instruments such as, for example, the FSM-6000, surface stress meter manufactured by Luceo Co., Ltd. (Tokyo, Japan) or the like.
For strengthened glass articles in which the compressive stress layers extend to deeper depths within the glass, the FSM technique may suffer from contrast issues that affect the observed DOL. At deeper DOL values, there may be inadequate contrast between the TE and TM spectra, thus making the calculation of the difference between TE and TM spectra—and accurately determining the DOL—more difficult. Moreover, the FSM software analysis is incapable of determining the compressive stress profile (i.e., the variation of compressive stress as a function of depth within the glass). In addition, the FSM technique is incapable of determining the depth of layer resulting from the ion exchange of certain elements such as, for example, ion exchange of sodium for lithium, that are present in the glass.